Switching regulator type power supplies are well known in the art. In such arrangements, a power transistor is connected in series between an unregulated DC source and a load. The voltage developed across the load is sensed and compared to a predetermined reference and the resulting control signal from the comparator is used to control the switching of the transistor in such a fashion that the output voltage appearing across the load is maintained relatively constant within the regulation band of the system.
It has been found that such prior art voltage regulator circuits suffer from a common defect. Specifically, until such time that the feedback voltage comes within the designed regulation band following initial start-up, the series switching transistor is maintained in a condition allowing a heavy current to flow therethrough from the source to the load. The associated power, if allowed for an excessive time interval, will exceed the dissipation rating of the series switching transistor, resulting in permanent damage thereto.
To obviate this problem, the present invention provides a means for controlling the "on-time" of the series switching transistor during the interval following the turning on of the power supply up until the sampled feedback voltage lies within the regulation band of the power supply. To achieve this end, there is provided an additional circuit, which, upon energization of the power supply, creates a series of pulses of successively increasing duration which are AND'ed together with the output from the conventional comparator means of the regulator, such that the series switching transistor is periodically turned on, but only for short periods of time so that the power dissipation rating of the switching transistor is not exceeded. However, when the normal sensed feedback voltage falls within the regulation band of the system, the output from the conventional comparator takes over and thereafter controls the turning on and off of the series switching transistor.
It is accordingly an object of the present invention to provide an improved switching transistor type voltage regulator for a power supply.
Another object of the invention is to provide an auxiliary control circuit for a switching transistor type power supply regulator which prevents damage to the switching transistor for the transient interval following the turning on of the system.
Still another object of the invention is to provide an auxiliary control circuit for a switching transistor type voltage regulator which allows the voltage developed across the load of the supply to be built up over a period of short increments until the output voltage lies within a predetermined regulation band.